Publication: Estudio de los Procesos de Taladrado en Estructuras Aeronáuticas: Desgaste de herramientas, calidad y control del daño en el componente
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2020-12
Defense date
2020-12-18
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Abstract
Las operaciones de taladrado tienen un gran impacto en los tiempos y costes de los
procesos de fabricación y montaje de estructuras aeronáuticas, debido al gran volumen
de uniones mecánicas que se realizan, la dificultad para mecanizar estos componentes
y los altos estándares de calidad requeridos.
En esta industria, destaca el uso de materiales compuestos, especialmente, reforzados
con fibras de carbono (CFRPs), que poseen excelentes propiedades mecánicas específicas
y una buena resistencia a la fatiga y a la corrosión. El mecanismo de arranque de material
que se produce en los CFRP, se caracteriza por cortes intermitentes de las fibras y la
fluctuación de las fuerzas de corte. Además, las herramientas sufren un desgaste severo
causado por la abrasividad y dureza de las fibras de carbono.
Por otro lado, en elementos estructurales con elevas y complejas cargas, se requiere el
uso de aleaciones de titanio y aluminio, por sus mejores propiedades mecánicas. Este
documento se centra en el estudio de las operaciones de taladrado en Ti por su menor
maquinabilidad debido a su elevada resistencia y dureza, baja conductividad térmica y
afinidad química con la mayoría de los materiales que se utilizan en la fabricación de
herramientas.
En los procesos de montaje, cuando se requiere la unión de dos o más componentes
formados por materiales compuestos y aleaciones metálicas, se denomina apilado
híbrido, cuyo mecanizado supone una gran complejidad. Esto se debe a la baja
maquinabilidad de los materiales y a las interacciones que se producen durante su
taladrado, pudiendo afectar a la calidad y a la integridad superficial del agujero.
En esta tesis se analizan, de forma experimental, diversas operaciones de taladrado
con herramientas de metal duro y recubrimiento de diamante para los procesos de
taladrado automático.
En los materiales compuestos CFRP se estudia la influencia de los parámetros de
corte en los mecanismos y evolución del desgaste de herramienta, así como en la
calidad y control del daño inducido por el mecanizado en el agujero. Este análisis
combinado permite optimizar las condiciones de corte y determinar la dependencia de
estas variables en avanzados estados de desgaste.
En cuanto a los apilados híbridos, en este documento se presenta un estudio sobre
la influencia de los niveles de lubricación MQL (Minimum Quantity Lubrication) en
los mecanismos de desgaste y la calidad de cada una de las capas que componen un
apilado Ti/CFRP/Ti.
La mejora de los procesos de taladrado en apilados híbridos y la optimización de
los niveles de lubricación MQL permiten realizar mayor cantidad de agujeros en una
única operación de taladrado (One Shot Drilling, OSD) e introducir técnicas de montaje
avanzadas.
Drilling operations have a huge impact of time and cost on aircraft structures manufacturing and assembly processes, owing to the big volume of mechanical joints used, the complexity of the machining operation and the quality standards required. In this industry, composite materials are used extensively, mainly, Carbon Fiber Reinforced Plastics (CFRPs), which stand out by their excellent specific mechanical properties and good fatigue and corrosion resistance. The material removal process is characterized by intermittent fracture of the fibers and oscillation of the cutting forces. Furthermore, the drill bits suffer a severe tool wear produced by the abrasiveness and hardness of the carbon fibers. On the other hand, structural elements with very demanding and complex loads are made of titanium and aluminum alloys for their superior mechanical properties. This document focuses on the analysis of Ti drilling due to its high hardness and strength, poor thermal conductivity and chemical affinity with most cutting tool materials, which result in a lower machinability. In assembly processes, components made from composite materials and Ti alloys are usually joined, producing hybrid stacks, which machining imposes an extra complexity. During drilling operations, interactions may occur between these different nature materials that may affect the quality and surface integrity of the hole. In this thesis, multiple drilling operations are analyzed, from an experimental point of view, with diamond coated carbide tools for automatic drilling processes. For CFRP drilling, it was studied the influence of the cutting parameters in tool wear mechanisms and evolution, as well as in the quality and control of the machining induced damage of the hole. This combined analysis allows to optimize cutting conditions and to determine the dependence of these variables under severe tool wear. Regarding hybrid stacks, this document focuses on the analysis of the Minimum Quantity Lubrication (MQL) level influence in tool wear mechanisms and the quality of each layer in a Ti/CFRP/Ti stack. The improvement of hybrid stacks drilling processes and the optimization of the MQL lubrication level, allows to perform more holes in a single drilling operation (One Shot Drilling, OSD) and to introduce advance assembly processes.
Drilling operations have a huge impact of time and cost on aircraft structures manufacturing and assembly processes, owing to the big volume of mechanical joints used, the complexity of the machining operation and the quality standards required. In this industry, composite materials are used extensively, mainly, Carbon Fiber Reinforced Plastics (CFRPs), which stand out by their excellent specific mechanical properties and good fatigue and corrosion resistance. The material removal process is characterized by intermittent fracture of the fibers and oscillation of the cutting forces. Furthermore, the drill bits suffer a severe tool wear produced by the abrasiveness and hardness of the carbon fibers. On the other hand, structural elements with very demanding and complex loads are made of titanium and aluminum alloys for their superior mechanical properties. This document focuses on the analysis of Ti drilling due to its high hardness and strength, poor thermal conductivity and chemical affinity with most cutting tool materials, which result in a lower machinability. In assembly processes, components made from composite materials and Ti alloys are usually joined, producing hybrid stacks, which machining imposes an extra complexity. During drilling operations, interactions may occur between these different nature materials that may affect the quality and surface integrity of the hole. In this thesis, multiple drilling operations are analyzed, from an experimental point of view, with diamond coated carbide tools for automatic drilling processes. For CFRP drilling, it was studied the influence of the cutting parameters in tool wear mechanisms and evolution, as well as in the quality and control of the machining induced damage of the hole. This combined analysis allows to optimize cutting conditions and to determine the dependence of these variables under severe tool wear. Regarding hybrid stacks, this document focuses on the analysis of the Minimum Quantity Lubrication (MQL) level influence in tool wear mechanisms and the quality of each layer in a Ti/CFRP/Ti stack. The improvement of hybrid stacks drilling processes and the optimization of the MQL lubrication level, allows to perform more holes in a single drilling operation (One Shot Drilling, OSD) and to introduce advance assembly processes.
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Keywords
Aeronáutica, Materiales compuestos con refuerzo de fibra de carbono, CFRPs, Taladrado automático, Máquinas herramienta, Carbon Fiber Reinforced Plastics, CFRP composites, CFRPs, Drilling